The present invention relates to a fluid pressure control device in which a solenoid valve is fixed to a housing with a simple structure and which is lightweight and can be manufactured at low cost.
FIG. 5 shows a conventional fluid pressure control device including a solenoid valve designated by numeral 1 in the figure. The solenoid valve 1 has a solenoid coil 2 and a frame 3 made of a magnetic material to function as a magnetic circuit. In the frame 3 is provided a fixed valve seat 4. By activating the solenoid coil 2, an armature 5, which is biased by a spring 6, is pulled by the magnetic force of the coil 2, so that a valve body 7 at the front end of the armature 5 moves away from the fixed valve seat 4. In this state, a fluid chamber 9 defined in front of the frame 3 communicates through a passage 8 with a fluid passage 11 (which is a discharge passage in this example).
A changeover valve 12 is mounted, together with the frame 3 of magnetic material, in a bore formed in a housing 10. This changeover valve comprises a sleeve 12b and a spool 12a. The spool 12a has a fluid passage having an orifice and moves in the sleeve 12b to a point at which the pressures acting on both ends thereof balance, thereby changing over the state of fluid communication between an inlet leading to a pressure source (not shown) and first and second outlets leading to wheel brakes. This type of changeover valve is well-known in the art. It is not important in the present invention whether or not the device includes such a changeover valve. Thus, its detailed description is omitted here.
The point is that, irrespective of whether the device includes the changeover valve 12 or not, the solenoid valve 1 shows a stronger tendency to come out of the bore in the housing as the fluid pressure in the fluid chamber 9 increases.
Thus, the device of FIG. 5 is provided with a seating plate 13 bolted to the housing 10 to prevent the solenoid valve 1 from coming out of the bore.
Unexamined Japanese Patent Publication 4-228985 discloses other ways to retain the solenoid valve in a fixed position. In one embodiment, a frame of a magnetic material has a flange which is bayonet-fitted in a groove having a larger diameter than an inlet formed by recessing the opening of the bore. In another embodiment, both the frame and the bore are threaded to keep them in threaded engagement with each other.
A fluid pressure control device for use in vehicle antilock or anti-spin control is required to be as small in size, lightweight and low-cost as possible. The device of FIG. 5 does not satisfy these requirements because it requires the seating plate 13 and the bolts for retaining the plate.
The device disclosed in Unexamined Japanese Patent Publication 4-228985 or the device in which the solenoid valve is screwed into the housing is high in manufacturing cost and low in mass-productivity.